Melting copper



Oct. 6, 1942.

P. M.v HULME ET AL MELTING COPPER Fiied April 5, 1941 INVENTORS PHILIPM. HULME ROBERT AGHELARDI .a '4. ATTORNEYS o ,BY

Patented Oct. 6, 1942 UNITED STATES PATENT QFFICE azoa'oss l -MELrlNGcorran v 'Pump M. unime and Robert A. Ghandi, rex-sn Amboy, N.' J.,assignors to International Smelting and Refining Company, a corporationof Montana Application Apru's, i941, serial No. 386,936

s claims. (cl. vs-ss) This invention relates to the melting of copper,and more particularly to the melting of copper chiey by radiant heat.The invention has for its principal object the provision of an improvedmethod for melting copper chiey by radiant 5 heat.

Proposals have heretofore been made to melt copper largely by'radiantheat, as, for example, in the United States patentto Betterton No.

2,065,207. The melting procedure of such prior l proposals has involvedintroducing the solid copper to. be melted into a pool or bath of moltencopper which is maintained in the molten state largely by radiant heat.Upon introduction into the molten bath, the solid copper sinks and hencel `substantially all of the heat required to melt the solid copper mustbesupplied by radiation to the surface of the molten bath. A

In contrast with such prior proposals, the

present invention contemplates exposing solidV copper to be melted to asource of radiant heat which is at a temperature at least approximatelyas high as the melting temperature of copper. lThe solid copper ismaintained thus exposed until it-becomes heated from its initialrelatively low temperature to an elevated temperature approaching itsmelting point. The heated but still solid copper is then introduced intoa bath of molten copper which is maintained in the molten state largelyby radiant heat.y Thus, in accord- 3 q K XA )Sedl--wli T24) 'Ei a-l inwhich q Net rate -of radiant heat transfer; A=Area of radiating surface;E1=Emissivity of radiating surface; E2=Emissivity of absorbing surface;

Ti=Absolute temperature of radiating surface; 5

and Tz=Absolute temperature of absorbing surface.

rf u; is assumed that the emissivity of theme1- ating surface is unity,then the foregoing equation may be rewritten to express the rate o! heattransferper unit of heat radiating area (q1)` as follows:

q1=KE2(Ti4- 24) From the latter equation it is seen that the rate ofheat transfer is proportional to the emissivity of the copper beingheated. v

We have found that theV emissivity of copper in the solid state is verymuch greater than the emissivity of molten copper. The emissivity ofmolten copper is only about 0.16, whereas the emissivity of solid copperin the formof commercial copper cathodes is about 0.6. In consequence ofthis difference in emissivities, solid copper will absorb radiant heatat a much higher rate vthan molten copper.

Based on these findings, the present invention provides an improvedmethod for melting copper by means of which the melting rate of thecopper is increased substantially over heretofore known melting methods.Briey stated, the method of the invention comprises exposing solid,relatively cold copper to a source of 'radiant heat at. a temperature atleast as approximately as high as the melting temperature of copper,maintaining the solid copper thus exposed until it has been heated to atemperature approaching its melting point, and introducing thethus-heated copper while still in the solid state into ya bath of moltencopper wherein said heated solid copper is melted by heat transferred tosaid bath chiefly by radi- A ation.

It will be observed that the increased melting rate obtainable inaccordance with the invention is greater than can be achieved by simplepreheating. The preheating of copper preparatory to melting has beenproposed heretofore, as, for example, in the United States patent toLukens et aLVNo. 1,733,419. The proposal set forth in the Lukens et al.patent (and other similar proposals) involves passing hot combustiongases in contact with solid copper preparatory'to introducing the copperinto a ymelting chamber heated by the combustion gases. Such apreheating operation takes advantage of the relatively large meantemperature difference between the combustion gases and cold solidcopper, which mean temperature difference is substantially greater thanthe mean temperature diierence between the combustion gases and a bathof molten-copper. As will be apparent from a consideration of theequations given above, the method of the invention takes advantage ofthis greater mean temperature dieren'ce between the solid copper and thesource of heat, in addition furnace under the hemd 'arch n. 4'rnccathodes lie for a short period of time on tables or ledges 2|, and inthis position they receive directly heat radiated from the arch l2.Owing to 'the high heated but still solid cathodes are then pushed ofmolten copper while still in the solid state yin order to promoteeillcient melting. 'I'he heated solid copper, being of greater densitythan molten copper, sinks to the bottom of the bath and there into thebath of molten copper.

For most eillcient operation it is desirable that the cathodes .remainon the ledges 24 until they have'been heated nearly to the meltingpoint, but little or n'o advantage is derived by keeping them longerinthis position. As soon as the surface of the cathodes begins to melt,the memelts more rapidly' than it would if allowed to y melt rst and nowin the molten state into the bath. There is no advantage in keeping thecopper out of the bath until it melts,because as soon as drops of moltenmetal coverl the surface. the

emissivity dropsto the value of .molten copper and the heating ratedrops correspondingly. By immersing the 'heated but still solid copperinto the bath of molten copper, the former is speedily -melted byintimate contact with the molten ma- A terlal. v The heat required forfusion is drawn from the reserve of heat in the molten bath and isreplaced by radiation or other mode of trans.

fer from the heating source to the bath.

The invention will be better understood from the following detailed-description considered in commotion with the accompanying drawing, in

which Fig. l is a longitudinal section through a furnace adapted forcarrying out the method of the invention; and

Fig. 2 is a vertical section taken substantially along the line 2-2 ofFig. 1.

The furnace shown in the drawingis a fuel fired munie furnace having amelting chamber l0 separated from a combustion chamber4 II by thedroplets, or sweat. -ofmolten copperthat A completely melted before thenext cathode is.

a refractory arch I2. The -melting chamber has a bottom or iloor Il, endwalls Il; and side walls l5 of more or less standard refractoryconstruc-y tion.l The combustion chamber likewise is en-` closed by arefractory-roof i6, refractory end walls l1, and refractory side wallsI8. Fuel is introduced into the combustion chamber through burners Il,and is burned in the combustion a depth indicated by the normal metalline L.

This pool .of copper is maintained at a suitable temperature above the'melting point `of copper chieily by heat radiated from the heated-mullle arch. I2, `although sonic heat Ais' of course con-1 the'refrac-65 ducted to the molten metal through toryalongthesidewall.

Copper, advantageously in the form of commercial copper cathodes C, isintroduced into the melting chamber Il of the furnacethrough chargingslots 23 located -in they furnace 'end walls. In charging, the cathodesare deposited on an inclined rack 23, and each cathode is pushed bythose behind itdownwardly along the 'rackthrough the charging slot andon to an insulted* ble 0r kille Il located Within 75 forms on cathodesurface. If the cathodes are pushed into the bath of molten copper afterbeing heated almost to the melting point but while still solid, theysink, and in the intimate Vcontact ofsubmergence in the molten metalthey are quickly melted by the reserve of heat in the molten bath. Therelatively small amount of -heat thus supplied to the cathodes by thebath is made up rapidly enough largely by radiation directly to thebath. y

It is understood that under some conditions of operation it may beundesirable or impractical to push the cathodes into the bath of moltenmetal before they have become partially or completeiy'melted. Forexample, if the rate at whichmolten coppe:` is withdrawn from thefurnace drops olf considerably, it may be necessary to charge thecathodes at a rate so slow that the cathodes on the ledges 2l becomepartially or advanced. v

Molten copper is withdrawn from the melting chamber I3 f through atapping hole4 2i, and thence overflows into a launder f 26, throughwhich it is passed to suitable casting equipment.

The melting method of the invention is well adapted foruse in caseswhere copper is melted under conditions inhibiting contamination of thecopper, that is, by melting the copper in an atmosphere substantiallyfree of injurious contaminants. To this end the atmosphere in themelting chamber I0 above the surface of the molten copper may be a gasmixture consisting essentially o'f carbon monoxide and nitrogen. Such agas mixture may be introduced through a pipe `21 communicating with the'interior of the melting chamber. In order to Aprevent excessive loss ofthe gaseous atmosphere through the charging slots 22, suitable' seals2l, which may be of the type described in our copending applicationSerial No. 362,956, nled October 26, 1940, may be mounted at theentrances to the slots.

v'l'.he melting rate for melting copper largely by radiant heat may bevery materially increased 'by the method of the invention. Aconsideration of the specific heat content of copper at varioustemperatures will serve to demonstrate the extent of the increasedmelting rate theoretically obtainable. For example, to heat one pound ofcopper from a temperature lof about F. to a temperature closelyapproaching its melting point requires absorption by the copper ofapproximately B. t. u. To melt the thus-heated copper and raise itstempermre to about 2200 F. (an average casting temperature) requiresabwith the method of the invention, however, the

greater part of the required heat is supplied largely byradiation'directly to the solid copper. In melting cathodes having anemissivity of about .6 under a muiiie arch having theoretically perfectemissivity., it is possible to supply the 190 B. t.'u. required forheating the metal to the melting point ata rate almost four times asfast as if the cold copper is charged directly into the molten pool.

We have found in'actual operation of a furnace that the theoreticalimprovements of the invention are amply achieved in practice. In afurnace in which the emissivity of the munie arch I2 is about 0.9, solidcathode copper on the ledge 24 is heated largely by radiant heat fromits initial temperature almost to the melting temperature at a rateabout three times as fast as if the cold solid copper is chargeddirectly into the molten bath.

It is understood that the foregoing description of a specic embodimentofv the invention with particular reference to a furnace constructed asshown in the drawing is byway of illustration only. The invention may becarried out with benecial results in furnaces of many different designs,and in various manners. To secure in some measure the advantagesv of theinvention itis necessary'only to make provision vfor exposing the solidmetal to a source of radiant heat for a suiiicient period of time toenable it to be heated almost to the melting point before introducing itinto a `We claim:

1. The method of melting copper chieiiy by radiant heat which comprisesexposing solid, relatively cold copper to be melted to a source ofradiant heat at a temperature at least approximately as high as themelting.- temperature of copper, maintaining the' solid copper thusexposed until it is heated to a temperature approaching its meltingtemperature, whereby advantage is taken of the relatively highemissivity of solid copper in heating the copper from its initialtemperature to the temperature approaching its melting point, andthereafter introducing the heated butstill solid copper into a bath ofmolten copper wherein said heated solid copper is melted by heattransferred to said bath chieiiy by radiation.

2. The method of melting copper under conditions inhibitingcontamination thereof 4which comprises exposing solid, relatively coldcopper in an atmosphere substantially free of injurious bath of themolten metal.

source of radiant heat at a temperature at least approximately as highas the melting temperature voi copper, maintaining the solid copper thusexposed until it has become heated to a temperature approaching itsmelting point, and introducing the thus-heated copper while still in thesolid state int'o a bath of molten copper wherein said heated solidcopper is melted by heat transferred to said bath chiefiy'by radiation.4. The method of melting copper chiefly by radiant heat which comprisesexposing solid,

relatively cold copperfto a source of radiant heat at a temperature atleast approximately as high as the melting temperature of copper,maintain- Aing the solid copper thus exposed until it has become heatedto a temperature approaching its melting point, and introducing thethus-heated copper while still in the solid state'into a bath of moltencopper exposed to and maintained-in the molten state chieiiy by radiantheat, whereby .the heat yrequired to heat the copper from its initialtemperature nearly to its melting point is supplied largely by radiationdirectly to solid copper. and in melting the copper only approxif matelyits heat of fusion is supplied by lradiation 4 to molten copper.

contaminants to a source of radiant heat at a A molten copper whereinsaid heated solid copper is melted by heat transferred to saidv bathchiefly.. by radiation. Y Y

3. The method 'of melting copper which comprises exposing solidrelatively cold copper to a 5. The method of melting copper chiefly byradiant heat and under conditions inhibiting contamination 'of the.copper which comprises exposing solid, relatively cold copper in anatmosphere substantially free of injurious contaminants to a source ofradiant heat at a temperature at least approximately as high as themeltingtem'perature of copper, maintaining the copper thus exposed insaid atmosphere until it has been heated to a temperature approachingits melting temperature, and introducing the thus-heated copper whilerstill in the solid state into a. bath of molten copper under anatmosphere free of injurious contaminants, said molten copper beingvexposed to and maintained in the molten state chiey by a source ofradiant heat at a temperature higher than themelting point Vof copper,whereby the heat required to heat the copper from its initialtemperatureV nearly to its melting point is supplied largely byradiation directly to the solid copper, and in melting the copper onlyvapproximately its heat of fusion is supplied by radiation to moltencopper.

6. The method of melting copper under conditions inhibitingcontamination thereof whichV comprises exposing solid, relatively coldcopper in an atmosphere consisting essentially of carbon monoxide andnitrogen to a. source of radiant heat at a temperature at leastapproximately as high as the melting temperature of copper,maintaining-the solid copper thus exposed until it is heated to atemperature approaching its melting temperature, and introducing thethusheated copper while still in the solid state into a bath of moltencopper wherein said heated solid copper is melted by heat transferred tosaid bath chiefly by radiation. Y

7. Themethod of melting commercial coppe vcatl'iodes which comprisesexposing the solid cathodes while relatively cold to a source o fradiant heat at a temperatureat least approximately as high as themelting point of copper, maintaining the solid cathodes thus exposeduntil they have become heated to a temperature approaching their meltingpoint, and introducing the thus-heated cathodes while still in the solidstate into a bath ofmolten copper wherein said 4 moco heated sona @modesare melted by ne.: mm-

'terredtosaidbathchieiiybyradintiom- 8. The method oi melting commercicl.copper cathcdes u nder conditions inhibitins teminetion thereof whichcomprises e the solid relatively cold cathodes in an atmospheresubvstanizia'lly free of injurious containment: to n source of radiantheat at a temperature at lent approximately ashish as the meltingpointu! Y copper,'ma.inta\inlns the solid cathodes thusexpoc'cdimtiltheyhsvcbecomeheatedtoetemspproachlnl their meltingpoint,and

